[RF] RooEffProd uses different names for the same proxy in the copy constructor

[Phmonski]

Explain what you would like to see improved and how.

The standard constructor and copy constructor of the RooEffProd class use the same proxy _eff with different names eff / acc.
This raises issues when exporting this class to JSON. Is it possible to harmonize these names to fix the issue?

ROOT version

6.37.01

Installation method

build from source

Operating system

ArchLinux

Additional context

No response

[guitargeek]

Sure, thanks for the catch! The next time you see inconsistencies like this, you can just open a PR if you want 🙂